Gas turbine engines are widely used for aircraft power, to generate electricity, to power ships, and to pump fluids.
In general gas turbines consist of a compressor section, a combustor and a turbine section. In the compressor section air is compressed to a temperature which may be more than 1000xc2x0 F. and a pressure which may be more than 300 psi. This heated compressed air is mixed with fuel and burned to produce hot gases which are expanded through a turbine which extracts energy. A portion of this extracted energy is used to power the compressor section but most of it is available for external uses.
The turbine section of the gas turbine engine is subject to many forms of deterioration. One form of deterioration is hot corrosion. Hot corrosion is a chemical attack of the turbine components. Hot corrosion usually involves a chemical attack by one or more compounds which contain one or more materials from the group comprising alkaline metals, vanadium and sulfur. These compounds attack the oxides which otherwise protects the superalloy turbine components from attack by oxygen. Hot corrosion generally occurs over the temperature range from 1300xc2x0 to 2200xc2x0 F.
Some of the ingredients which participate in hot corrosion, the previously mentioned alkaline metals, vanadium, and sulfur are often found in the fuel (particularly sulfur and vanadium) and some often come from the external atmosphere (alkaline elements). The external atmosphere is particularly conducive to hot corrosion when the engine is operated in a maritime environment and the atmosphere contains sea water in aerosol form.
It was previously generally believed that the sea water aerosl passed through the compressor without much affect and directly interacted into the turbine components to induce corrosion. It is now believed that while such flow through the compressor occurs, it is not directly responsible for most hot corrosion. Instead, it appears that the major contributor to turbine section hot corrosion by sea water aerosol particles results from a mechanism which includes the build up from salt on the later compressor stage blades and vanes and the subsequent flaking of the salt from the blades and vanes and its passage through the combustor and into the turbine as sizable solid particles. These sea salt particles adhere to the hot turbine component surfaces and cause accelerated localized corrosion. This adherence of concentrated sea salt particles on the turbine surfaces is apparently the most significant contributor to corrosion.
1. Field of the Invention
This invention relates to a coating for compressor components which reduce the build up of salt and thereby reduce turbine hot corrosion resulting from the passage of concentrated salt particles through the engine.
2. Description of Related Art
Applicants are unaware of any art which is truly related to this invention in as much as this theory is a new explanation for hot corrosion phenomenon in gas turbines. Prior attempts to reduce hot corrosion have focused on the materials used in the turbine section, the coatings and the underlying substrate materials. Efforts have been made to design coatings and substrate materials which have higher inherent corrosion resistance by adjusting the chemical composition. Applicants have no knowledge that anyone has attempted to reduce turbine hot corrosion by coating compressor component surfaces.
Accordingly it is an object of the present invention is to provide a coating for gas turbine compressor components which reduces the build up of salt on such components and thereby reduce hot corrosion in the turbine section. It is also an object of the invention to provide a method of applying such a non wetting coating of gas turbine compressor components.
According to the invention, gas turbine compressor blades, vanes and other hardware is coated with a thin adherent coating which is not appreciably wetted by sea water. Since the sea water wets the blade only minimally, it remains in the form of essentially spherical droplets rather than spreading out on the blade on the components as a sheet of liquid. This maintenance of the drop like geometry reduces the relative surface area of the sea water and reduces the deposition of salt onto the compressor component surfaces. Thus the droplets of sea water tend to pass directly through the engine without forming concentrated areas rich in sea salt on the turbine blades. The invention coating comprises a mixed glassy semi crystalline oxide coating consisting of 10-90% by vol. wherein the ratio of aluminum to zirconium is from 1:10 to 10:1.